In a mouse study, a Vaxfectin(R)-formulated vaccine containing a peptide from Tyrosinase-Related Protein 2 (TRP-2), an antigen commonly expressed by several types of tumors including glioma and melanoma, resulted in approximately a 100-fold increase in antigen-specific CD8+ T-cell responses compared with unformulated vaccine. CD8+ T-cells are deployed by the immune system to identify and destroy infected or cancerous cells.

Vaxfectin(R)-formulated Protein Vaccines

Vical has previously reported that data from studies in mice demonstrated the potential of the Vaxfectin(R) adjuvant to be used as a dose-sparing agent with protein-based commercial seasonal influenza vaccine and with protein-based H5N1 pandemic influenza vaccine currently stockpiled by the U.S. government. Vaxfectin(R)-formulated vaccine produced higher antibody responses than up to 10-fold higher doses of unformulated vaccine. Dose-sparing could be critical in extending limited vaccine supplies to protect the greatest number of people in the event of a pandemic influenza outbreak.

Data from additional studies in mice presented for the first time today demonstrated that Vaxfectin(R)-formulated seasonal influenza vaccine generated broader, more balanced antibody responses than unformulated vaccine, and also generated influenza-specific T-cell responses. Adjusting the ratio of Vaxfectin(R) to vaccine drove substantial increases in either antibody or T-cell responses, without reducing the other type of response, compared with unformulated vaccine. The ability to favor primarily antibody or T-cell responses could provide important advantages in developing vaccines for specific applications.

H5N1 Pandemic Influenza Vaccine Phase 1 Trial Update

Vical reported in July that the company's Vaxfectin(R)-formulated H5N1 pandemic influenza DNA vaccines achieved potentially protective levels of antibody responses (H5 hemagglutination inhibition, or HI, titers of at least 40 and at least a four-fold increase from baseline) in at least 50% and up to 67% of evaluable subjects in the higher dose cohorts in a 100-subject Phase 1 trial.

Following injections at Days 0 and 21, responses peaked by Day 56, and more than 90% of the responders had sustained responses through the last measurement (Day 84) at the time of the preliminary analysis. Expanded data presented today shows that in the two cohorts receiving the highest H5 DNA dose (1 mg), 80% to 100% of the responders had sustained responses through Day 182. Similar results for a vaccine deployed during the early stages of a pandemic outbreak could provide substantial protection to the at-risk population and potentially alter the course of the pandemic.

These results support further development of Vaxfectin(R)-formulated DNA vaccines, and could position them as potential alternatives to conventional vaccines. DNA vaccines are fundamentally different from conventional vaccines because they do not contain any part of the virus itself, and may offer compelling advantages in response to a pandemic outbreak because of significantly reduced development and manufacturing times. Vical is currently seeking funding to continue development of a pandemic influenza vaccine candidate.

"Through independent and collaborative research, we have demonstrated Vaxfectin(R)'s ability as an adjuvant to increase antibody and/or T-cell responses with DNA vaccines and with protein- and peptide-based vaccines," said Dr. Rolland. "We are advancing with development of our own Vaxfectin(R)-formulated product candidates and are exploring opportunities with potential collaborators and commercial partners for development of additional infectious disease and cancer applications for this novel adjuvant."

About Vical

Vical researches and develops biopharmaceutical products based on its patented DNA delivery technologies for the prevention and treatment of serious or life-threatening diseases. Potential applications of the company's DNA delivery technology include DNA vaccines for infectious diseases or cancer, in which the expressed protein is an immunogen; cancer immunotherapeutics, in which the expressed protein is an immune system stimulant; and cardiovascular therapies, in which the expressed protein is an angiogenic growth factor. The company is developing certain infectious disease vaccines and cancer therapeutics internally. In addition, the company collaborates with major pharmaceutical companies and biotechnology companies that give it access to complementary technologies or greater resources. These strategic partnerships provide the company with mutually beneficial opportunities to expand its product pipeline and address significant unmet medical needs. Additional information on Vical is available at www.vical.com.

This press release contains forward-looking statements subject to risks and uncertainties that could cause actual results to differ materially from those projected. Forward-looking statements include statements about the results of the company's Vaxfectin(R)-formulated H5N1 influenza DNA vaccine Phase 1 clinical trial, the results of nonclinical mouse studies of Vaxfectin(R)-formulated protein-based influenza vaccines, and the results of a nonclinical mouse study of a Vaxfectin(R)-formulated TRP-2 peptide cancer vaccine. Risks and uncertainties include whether H5N1 influenza DNA vaccine Phase 1 clinical trial results will be confirmed in larger studies; whether nonclinical results from mouse studies will advance to human clinical testing, and if so, whether such testing will yield similar results; whether DNA vaccines against H5N1 influenza or any other targets will be successfully developed and commercialized; whether DNA vaccines will become alternatives to conventional vaccines; whether Vical or others will secure funding to advance the pandemic influenza DNA vaccine program; whether commercial partners or collaborators will pursue additional Vaxfectin(R) applications; whether any product candidates will be shown to be safe and efficacious in clinical trials; the timing of clinical trials; whether Vical or its collaborative partners will seek or gain approval to market any product candidates; the dependence of the company on its collaborative partners; and additional risks set forth in the company's filings with the Securities and Exchange Commission. These forward-looking statements represent the company's judgment as of the date of this release. The company disclaims, however, any intent or obligation to update these forward-looking statements.